Filter underdrain assembly and method of producing same

ABSTRACT

A filter underdrain assembly employs a perforated strainer body having a surface configuration providing circumferentially extending recesses. A fabric covering on the strainer body serves to separate particulate matter from the liquid passing therethrough, and plaiting of the fabric directly upon the surface of the strainer body results in interengagement therebetween. This reduces the normal tendency for relative axial movement to occur between the fabric covering and the body, particularly during backwashing operations.

United States Patent Hunter et al.

[54] FILTER UNDERDRAIN ASSEMBLY AND METHOD OF PRODUCING SAME [72]Inventors: Bruce H. Hunter, 53 Oak Road, 6

Long Meadow, Mass. 01106; Norbert L. Reiner, 21 Blakeslee Road,Wallingford, Conn. 06492 6/1967 Balletal..... ..2l0/497X [151 3,685,6571451 Aug. 22, 1972 Miller, Jr. et al. ..210/497. 1- X Harms et al...210/323 Primary Examiner-Samih N. Zahama Attorney-Peter L. Costas [57]ABSTRACT A filter underdrain assembly employs a perforated strainer bodyhaving a surface configuration providing circumferentially extendingrecesses. A fabric covering on the strainer body serves to separateparticulate matter from the liquid passing therethrough, and plaiting ofthe fabric directly upon the surface of the strainer body results ininterengagement therebetween. This reduces the normal tendency forrelative axial movement to occur between the fabric covering andthebody, particularly during backwashmg operations.

9 Claim, 6 Drawing Figures PATENTEUwczz can 3.685.657

2 Inren furs I L Hr I Norerf L Reine/- i w 2, v I Bruce #Humer F IG. 6B9 Z W 4 Harney BACKGROUND OF THE INVENTION In filtration systems forcleaning the water of swimming pools and the like, it is common practiceto employ a tank or other container filled with a particulate filtrationmedium. In certain cases, the apparatus previously employed has reliedfor filtration upon a layer of diatomaceous earth or similar fineparticulate material deposited upon one or more appropriate memberswithin the tank. However, the efficient use of such apparatus requiresthat the deposits be removed periodically from the support surfaces toprevent clogging and to ensure satisfactory filtration, and in manyinstances complete removal thereof has proven quite impracticable byconvenientand conventional (i.e., backwashing) techniques. Other systemsemployed have relied upon a bed of sand, charcoal or other finelydivided materials to provide the primary filtering effect, and suchsystems conventionally utilize a filter underdrain for the purpose ofstraining or separating theparticulate filter medium from the liquidpassing therethrough, so as to provide a purified vfiltrate, free ofsolid particles, for reuse.

Filter underdrains have previously beenprovided by a variety ofdifferent structures including devices fabricated of sandstone or otherporous minerals, perforated stainless steel members, slottedpipes,and'the like. However, serious difficulties have been experienced withunderdrains of such types. The porous mineral structures tend to be veryfragile and prone to breakage even in normal handling and use. Metallicmembers are relatively expensive, difficult to install satisfactorily,often quite inaccessible for cleaning and maintenance once in place, andalso relatively weak as a result of the slotting or other modificationsthat are necessary to provide sufficient area for adequate filtration.Moreover, in substantially every type of underdrain previouslyavailable, the tendency for clogging has been relatively great, anddislodgingof the particles to unclog the drain'has typically beendifficult, inefficient and/or detrimental to the device in some respect.

Accordingly, it is an object of the present invention to provide a noveland efficient filter underdrain assembly for use with a particulatefiltration medium, which underdrain assembly has a high flow capacityand good straining characteristics, and in which any tendency forleakage and for bypass of the fabric by the particles of the filtrationmedium is minimized.

ltis also an object of the invention to provide such an underdrainassembly that is durable, that is relatively facile and inexpensive tomanufacture, and that enables rapid and convenient cleaning of thefabric to remove particulate matter which may become lodged therein.

Another object of the invention is to provide a novelmethod for theproduction of a filter underdrain assembly having the foregoingcharacteristics and advantages, which method is relatively facile andinexpensive to carry out.

SUMMARYOF THE INVENTION It has now been found that the foregoing andrelated objects can be readily attained in a filter underdrain assemblycomprising a tubular strainer body having a perforated sidewall with anexterior surface providing a multiplicity of circumferentially extendingrecessed portions therein. The strainer body has a fabric covering offilaments plaited directly upon its exterior surface and extendingentirely thereabout over substantially the entire length thereof. Thefabric covering conforms closely to the contour of the strainer surfaceso as to interengage with the strainer body in the recessed portionsthereof and to resist the occurrence of relative axial movementtherebetween. The assembly also includes means communicating with theinteriorof the body for connection to a pump, whereby particulate matterentrained in liquids passing into the interior of the strainer bodythrough the fabric covering are removed thereby.

In the preferred embodiments of the invention the strainer body isgenerally cylindrical, with an outside diameter that alternates alongthe length thereof between a relatively large and a relatively smalldimension; this provides a series of circumferential recesses extendingentirely about the body. Most desirably, the connection means ispositioned adjacent one end of the body and the assembly additionallyincludes an end plug inserted into the other end of the body and bondedto the inside surface of the sidewall to effect a seal thereat. Tonecessitate passage through the fabric covering of the entire volume ofliquid entering into the body interior, the fabric covering extendsabout the body at least between the connection means and the plug bondarea. Both the strainer body and the fabric covering may be fabricatedof a synthetic resinous material to afford considerable advantages inaccordance herewith and the material of the fabric is most desirably apolyester resin.

Certain objects of the invention may be attained in accordance with themethod wherein a tubular strainer member is fabricated, having aperforated sidewall with an exterior surface providing a multiplicity ofcircumferentially extending. recesses therealong. A fabric covering offilaments is plaited directly upon and in close conformity to thecontour of the exterior surface, with the fabric covering extendingentirely about the strainer member over substantially the entire lengththereof. Means communicating with the interior of the strainer memberfor connection to a pump is provided, and the fabric covering is capableof effecting the removal of entrained particulate matter from liquidspassing therethrough and through the sidewall of the strainer memberinto the interior thereof. Preferably, the method additionally includesthe steps of applying a length of water impermeable material about thestrainer member and fabric covering intermediate the ends thereof, andof severing the length of material, covering, and strainer memberintermediate the ends in the production of a plurality of underdrainsubassemblies. In such a method one of such communicating means isprovided on each of the subassemblies to produce a strainer assemblytherefrom. Most desirably, the method includes the steps of mountingconnection means adjacent one end of the strainer member, and of sealingthe other end of the strainer member by inserting an end plug thereintoand bonding the plug to the inside surface of the sidewall of thestrainer member.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of afilter underdrain assembly embodying the present invention;

FIG. 2 is a sectional view of the assembly of FIG. 1;

FIG. 3 is an end view thereof illustrating the female adapter thereof;

FIG. 4 is an opposite end view illustrating the end cap thereof;

FIG. 5 is an elevational view drawn to a reduced scale and illustratingthe filter underdrain assembly installed in a filtration tank that isfitted with a backwash valve, the tank and valve being shown in phantomline; and

FIG. 6 is an elevational view drawn to a reduced scale and illustratinga double length strainer tube having a filter fabric covering plaitedthereover, as used in the production of the illustrated underdrainassembly in accordance with the novel method hereof.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Turning now indetail to FIGS. 1-5 of the appended drawing, therein illustrated is afilter underdrain assembly embodying the present invention and generallydesignated by the numeral 10. As is seen in FIG. 5, the assembly 10 isadapted for installation in a tank 12 containing sand or some otherfiltration medium 13, and the assembly 10 is attached to a backwashvalve 14, the tank 12, sand 13 and valve 14 all being shown in phantomline. In one position of the valve 14, water is admitted into the tank12, through conduit 15, passes through the medium 13 for filtration, andthen exits through the underdrain 10, which separates entrainedparticles of the medium 13 and returns the water in a purified conditionfor reuse. In a second position of the valve 14, water passes into thetank 12 through the underdrain 10 to dislodge any particles of thefiltration medium 13 that may have become lodged therein (thebackwashing operation).

FIGS. 1-4 more clearly illustrate the construction of the underdrainassembly 10, which consists of a perforated elongated strainer tube 16having an axially undulating outer surface 18 that is provided bycircular portions that alternate along the length of the tube between arelatively large and a relatively small diameter to provide recesses inthe reduced diameter portions. Plaited directly and snugly upon theouter surface 18 of the strainer tube 16 is a fabric covering 20, whichclosely follows the contours of the outer surface 18 and is therebyinterengaged with the tube 16 to substantially prevent relative axialmovement.

A female adapter 22 having an internally threaded portion 23 is securedover the fabric covering and strainer tube 16 at one end thereof, and isbonded by adhesive 24 to form a seal therewith; normally, the adhesivewill also extend under the adapter 22 to further enhance the seal andprevent leakage. A length of water-impermeable tape 26 is secured aboutthe opposite end of the tube 16 and an end cap 28 having an axiallyextending circular recess or channel 32 in its inner end is assembledthereon, with the central plug portion 30 being inserted into the tube16. The associated portion of the tube 16, fabric 20 and tape 26 seatwithin the recess 32 of the cap 28 between the plug portion 30 and outerlip portion. To ensure against leakage about the cap 26 (which mightultimately cause its disengagement), and adhesive material 34 isprovided between the central plug portion 30 and the inside surface 36of the tube 16; this bonded area serves to seal the end of the assembly10 and to avoid entry of water between the mating surfaces of the tube16 and cap 26.

In accordance with a preferred method of producing the type ofunderdrain assembly herein disclosed, a double length of strainer tube(not visible) may be employed and plaited with fabric covering 20, asillustrated in FIG. 6. Tape 26 is secured in a double width intermediatethe ends of the double tube to provide a subassembly 38, which may besevered along line A--A to provide the combination of strainer tube 16,fabric covering 20, and tape 26, upon which may be mounted the endmembers 22 and 26 to produce the underdrain assembly 10 of FIGS. l-5.

The materials utilized in the manufacture of the underdrain assemblydisclosed herein may vary considerably and will be quite apparent tothose skilled in the art. Normally, a synthetic resinous material ofeither thermoplastic or thermosetting nature will be employed for thebody of the assembly due to the facility and economy with which suchmaterials may be fabricated into the desired configuration, and also dueto the resistance to wear and deterioration which such resins afford.Although a considerable number of different types of synthetic resinsmight be appropriate, the polyolefines such as polyethylene andpolypropylene have been found to serve admirably because of their inertcharacteristics, facile forming characteristics and relatively low cost.

The material utilized as the fabric sleeve upon the body is alsodesirably provided by a synthetic resin, and a wide variety ofappropriate polymers are available. However, it has been found thatfabrics produced from polyester fibers, such as polyethyleneterephthalate, provide good filtration characteristics, while at thesame time offering very desirable flow rates and a level of strengththat results in a long useful life for the assembly. Certain syntheticfabrics, such as those fabricated of nylon filaments, are somewhat lessdesirable since they have a tendency to swell in water, which isgenerally absent in the polyester-type fabrics.

The end members and adapters used in the underdrain will normally befabricated of synthetic resinous materials, the choice of which willdepend somewhat upon the materials used for the body and fabriccovering. Although common masking tape (desirably coated with awater-proof adhesive) may be employed to secure the ends of the fabricduring assembly operations, a vinyl tape is more appropriately used toprovide a higher degree of protection against leakage. It is importantthat, when such a tape element is utilized, it not be of awater-permeable material since water seeping under the end members wouldtend to loosen the member and promote its disengagement. Of course, alladhesives employed should be of a waterproof type.

In use, it has been found that the underdrain assembly herein describedoffers more efficient filtration than do comparable prior art devices,and considerably higher rates of flow. In some instances, tests haveshown that as much as 50 percent more water can be filtered, per unit oftime, utilizing an underdrain assembly constructed in accordance withthe invention as compared with underdrains of the prior art.

in terms of durability, an underdrain assembly of the present type(utilizing a polyolefin body with polyester fabric covering plaitedthereon) has exhibited a useful life greatly in excess of any comparabledevice or assembly heretofore known. Tests were performed utilizing suchan underdrain assembly in a simulated installation, and a cycle whereinwater was drawn through the underdrain for four minutes followed by abackwashing operation effected for 1 minute. The underdrain wassubjected to 900 cycles without any evidence of lessened effectivenessof damage to any part of the assembly. In a typical swimming poolinstallation, the underdrain would be subjected to approximately 40backwash cycles per year, indicating that its useful life may oftenexceed that of the filter or of the swimming pool itself.

Thus, it can be seen that the present invention provides a novel andefficient filter underdrain assembly for use with a particulatefiltration medium, which assembly has a high flow capacity and goodstraining characteristics and which minimizes any tendency for leakageand for bypass of the fabric by the particles of the filtration medium.The invention provides a durable assembly that is relatively facile andinexpensive to manufacture and in which the fabric may be rapidly andconveniently cleaned to remove particles which may become lodgedtherein. The method utilized to produce underdrain assemblies having theforegoing characteristics and advantages is novel and is relativelyfacile and inexpensive to carry out.

Having thus described the invention, we claim:

1. A filter underdrain assembly comprising a tubular strainer bodyhaving a perforated sidewall with an exterior surface providing amultiplicity of circumferentially extending recessed portions therein; afabric covering of filaments plaited directly upon said exterior surfaceand extending entirely about said strainer body over substantially theentire length thereof, said fabric covering conforming closely to thecontour of said strainer surface to interengage with said body in saidrecessed portions and to resist relative axial movement between saidcovering and said body; and means communicating with the interior ofsaid body for connection to a pump, said fabric covering effecting theremoval of entrained particulate matter from liquids passing throughsaid covering and said sidewall of said body into the interior thereof.

2. The assembly of claim 1 wherein said body is generally cylindricalwith an outside diameter that alternates along the length thereofbetween a relatively large and a relatively small diameter, to provide aseries of circumferential recesses therein extending entirely about saidbody.

3. The assembly of claim 2 wherein said connection serted into the otherend of said body and bonded to the inside surface of said sidewall toseal said other end of said body, said fabric covering extending aboutsaid body at least between said connection means and the area of bond wisaid lu o neces itate assa e through said fabr i d coveri ng o theentire vol me f liquid entering into the interior of said body.

4. The assembly of claim 1 wherein said body and said fabric coveringare each fabricated of synthetic resinous materials.

5. The assembly of claim 1 wherein the synthetic resinous material ofsaid fabric is a polyester.

6. In a method for producing a filter underdrain assembly, the stepscomprising:

a. fabricating a tubular strainer member having a perforated sidewallwith an exterior surface providing a multiplicity of circumferentiallyex-' tending recesses therealong;

b. plaiting a fabric covering of filaments directly upon and in closeconformity to the contour of said exterior surface with said fabriccovering extending entirely about said strainer member oversubstantially the entire length thereof, said close conformity causinginterengagement of said fabric covering with said strainer member insaid circumferential recesses to resist relative axial movementtherebetween; and

. providing on said strainer member means communicating with theinterior thereof for connection to a pump, said fabric covering beingcapable of effecting the removal of entrained particulate matter fromliquids passing through said fabric covering and said sidewall of saidstrainer member into the interior thereof.

7. The method of claim 6 wherein said strainer member is provided insaid fabricating step with an outside diameter that alternates along thelength thereof between a relatively large and a relatively smalldiameter to provide a series of circumferential recesses extendingentirely about said body, said fabricating step additionally involvingextrusion of a synthetic resinous material through a generally annulardie opening to produce a generally cylindrical strainer member.

8. The method of claim 6 wherein said strainer member and covering arerelatively long, and additionally including the steps of applying alength of water-impermeable material about said strainer member and saidfabric covering intermediate the ends thereof, severing said length ofmaterial, fabric covering and strainer member intermediate said ends toproduce a plurality of underdrain subassemblies, and of providing one ofsaid communicating means on each of said subassemblies to produce astrainer assembly therefrom.

9. The method of claim 7 wherein there are included the additional stepsof mounting connection means adjacent one end of said strainer memberand of sealing the other end of said strainer member by inserting an endplug thereinto and bonding said plug to said inside means is adjacentone end of said body and wherein Surface Ofsaid sidewall ofsaid Strainermembersaid assembly additionally includes an end plug in-

1. A filter underdrain assembly comprising a tubular straiNer bodyhaving a perforated sidewall with an exterior surface providing amultiplicity of circumferentially extending recessed portions therein; afabric covering of filaments plaited directly upon said exterior surfaceand extending entirely about said strainer body over substantially theentire length thereof, said fabric covering conforming closely to thecontour of said strainer surface to interengage with said body in saidrecessed portions and to resist relative axial movement between saidcovering and said body; and means communicating with the interior ofsaid body for connection to a pump, said fabric covering effecting theremoval of entrained particulate matter from liquids passing throughsaid covering and said sidewall of said body into the interior thereof.2. The assembly of claim 1 wherein said body is generally cylindricalwith an outside diameter that alternates along the length thereofbetween a relatively large and a relatively small diameter, to provide aseries of circumferential recesses therein extending entirely about saidbody.
 3. The assembly of claim 2 wherein said connection means isadjacent one end of said body and wherein said assembly additionallyincludes an end plug inserted into the other end of said body and bondedto the inside surface of said sidewall to seal said other end of saidbody, said fabric covering extending about said body at least betweensaid connection means and the area of bond with said plug to necessitatepassage through said fabric covering of the entire volume of liquidentering into the interior of said body.
 4. The assembly of claim 1wherein said body and said fabric covering are each fabricated ofsynthetic resinous materials.
 5. The assembly of claim 1 wherein thesynthetic resinous material of said fabric is a polyester.
 6. In amethod for producing a filter underdrain assembly, the steps comprising:a. fabricating a tubular strainer member having a perforated sidewallwith an exterior surface providing a multiplicity of circumferentiallyextending recesses therealong; b. plaiting a fabric covering offilaments directly upon and in close conformity to the contour of saidexterior surface with said fabric covering extending entirely about saidstrainer member over substantially the entire length thereof, said closeconformity causing interengagement of said fabric covering with saidstrainer member in said circumferential recesses to resist relativeaxial movement therebetween; and c. providing on said strainer membermeans communicating with the interior thereof for connection to a pump,said fabric covering being capable of effecting the removal of entrainedparticulate matter from liquids passing through said fabric covering andsaid sidewall of said strainer member into the interior thereof.
 7. Themethod of claim 6 wherein said strainer member is provided in saidfabricating step with an outside diameter that alternates along thelength thereof between a relatively large and a relatively smalldiameter to provide a series of circumferential recesses extendingentirely about said body, said fabricating step additionally involvingextrusion of a synthetic resinous material through a generally annulardie opening to produce a generally cylindrical strainer member.
 8. Themethod of claim 6 wherein said strainer member and covering arerelatively long, and additionally including the steps of applying alength of water-impermeable material about said strainer member and saidfabric covering intermediate the ends thereof, severing said length ofmaterial, fabric covering and strainer member intermediate said ends toproduce a plurality of underdrain subassemblies, and of providing one ofsaid communicating means on each of said subassemblies to produce astrainer assembly therefrom.
 9. The method of claim 7 wherein there areincluded the additional steps of mounting connection means adjacent oneend of said strainer member and of sealing the other end of saidstrainer member by inseRting an end plug thereinto and bonding said plugto said inside surface of said sidewall of said strainer member.